Wood composites are among the world's most significant renewable materials. The most common wood composites produced today are oriented strandboard (OSB), plywood, and particle board. Waxes are commonly used in the production of wood composites. The production of wood composites generally includes the blending of dried wood strands and/or particles with a suitable oil-derived liquid wax formulation and an adhesive (resin). These materials are generally derived from non-renewable sources. The wax component may provide water repellant properties that reduce swelling of composites during periods of elevated environmental humidity. The resin components bind wood strands and/or particles to form the composite structures. The addition of wax components to the wood composites is thought to improve the mechanical and physical properties of the panels.
Generally, after blending the wood feedstock with a wax emulsion and a resin, the wood composite is formed by applying suitable pressure at elevated temperatures. Optimal application of pressure and temperature levels are determined from the specifications of the wax and resin components used, the type of composite being produced, and the tree species from which the wood fibers and/or strands and/or particles are produced. Once the wood composites are produced, a number of quality/performance characteristics are determined including, thickness swell, water adsorption, modulus of rupture, modulus of elasticity, internal bond, among others. The testing protocols for each type of wood composite have been well-defined by the respective regulatory bodies. Examples of these standards include: the Canadian Standards Association (CSA) O112.6-M1977 Phenol and Phenol-Resorcinol Resin Adhesives for Wood (High-Temperature Curing), the CSA O437.1-93 Test Methods for OSB and Waferboard, or the CSA Standard O151-04 Canadian softwood plywood. Before the commercialization of new resin (adhesive) it is usually necessary for them to meet the established standards such as the ones listed above.
Native lignin is a naturally occurring amorphous complex cross-linked organic macro-molecule that comprises an integral component of all plant biomass. Extracting native lignin from lignocellulosic biomass during pulping generally results in lignin fragmentation into numerous mixtures of irregular components. Furthermore, the lignin fragments may react with any chemicals employed in the pulping process. Consequently, the generated lignin fractions can be referred to as lignin derivatives and/or technical lignins. As it is difficult to elucidate and characterize such complex mixture of molecules, lignin derivatives are usually described in terms of the lignocellulosic plant material used, and the methods by which they are generated and recovered from lignocellulosic plant material, i.e. hardwood lignins, softwood lignins, and annual fibre lignins.
Given that lignin derivatives are available from renewable biomass sources there is an interest in using these derivatives in certain industrial applications. For example, lignin derivatives obtained via organosolv extraction, such as the Alcell® process (Alcell is a registered trademark of Lignol Innovations Ltd., Burnaby, BC, CA), have been used in rubber products, adhesives, resins, plastics, asphalt, cement, casting resins, agricultural products, oil-field products and as feedstocks for the production of fine chemicals. It has been suggested to use lignin-modified phenol-formaldehyde resin as an adhesive for wood composites (see, for example, U.S. Pat. No. 5,010,156; WO93/21260; WO94/24192).
However, large-scale commercial application of the extracted lignin derivatives, has been limited due to, for example, the inconsistency of their chemical and functional properties. This inconsistency may, for example, be due to changes in feedstock supplies and the particular extraction/generation/recovery conditions. These issues are further complicated by the complexity of the molecular structures of lignin derivatives produced by the various extraction methods and the difficulty in performing reliable routine analyses of the structural conformity and integrity of recovered lignin derivatives.
Despite the advantages of lignin, for a variety of reasons, it has not been adopted for widespread use in wood composites. For instance, it is often problematic to provide lignins that have acceptable and consistent performance characteristics. Additionally, the cost of producing and/or purifying the lignin may make it uneconomic for certain uses. Furthermore, incorporation of high levels of lignin in phenol-formaldehyde resin can lead to undesirably high end-point viscosities.